TY - JOUR
T1 - Linearity of Outgoing Longwave Radiation
T2 - From an Atmospheric Column to Global Climate Models
AU - Zhang, Yi
AU - Jeevanjee, Nadir
AU - Fueglistaler, Stephan
N1 - Funding Information:
N. J. thanks R. Pincus for feedback at an early stage of this work. Y. Z. acknowledges support under award NA18OAR4320123 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration or the U.S. Department of Commerce. S. F. acknowledges support from National Science Foundation Awards NSF PIRE‐1743753 and AGS‐1733818. We thank Daniel Koll for developing PyRADS code and making it publicly available ( https://github.com/ddbkoll/PyRADS ). We acknowledge the World Climate Research Programmes Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Figure 1 of this paper) for producing and making available their model output. For CMIP, the U.S. Department of Energy's Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals.
Funding Information:
N. J. thanks R. Pincus for feedback at an early stage of this work. Y. Z. acknowledges support under award NA18OAR4320123 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration or the U.S. Department of Commerce. S. F. acknowledges support from National Science Foundation Awards NSF PIRE-1743753 and AGS-1733818. We thank Daniel Koll for developing PyRADS code and making it publicly available (https://github.com/ddbkoll/PyRADS). We acknowledge the World Climate Research Programmes Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Figure 1 of this paper) for producing and making available their model output. For CMIP, the U.S. Department of Energy's Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals.
Publisher Copyright:
©2020. American Geophysical Union. All Rights Reserved.
PY - 2020/9/16
Y1 - 2020/9/16
N2 - The linearity of global-mean outgoing longwave radiation (OLR) with surface temperature is a basic assumption in climate dynamics. This linearity manifests in global climate models, which robustly produce a global-mean longwave clear-sky (LWCS) feedback of 1.9 W/m2/K, consistent with idealized single-column models (Koll & Cronin, 2018, https//:doi.org/10.1073/pnas.1809868115). However, there is considerable spatial variability in the LWCS feedback, including negative values over tropical oceans (known as the “super-greenhouse effect”) which are compensated for by larger values in the subtropics/extratropics. Therefore, it is unclear how the idealized single-column results are relevant for the global-mean LWCS feedback in comprehensive climate models. Here we show with a simple analytical theory and model output that the compensation of this spatial variability to produce a robust global-mean feedback can be explained by two facts: (1) When conditioned upon free-tropospheric column relative humidity (RH), the LWCS feedback is independent of RH, and (2) the global histogram of free-tropospheric column RH is largely invariant under warming.
AB - The linearity of global-mean outgoing longwave radiation (OLR) with surface temperature is a basic assumption in climate dynamics. This linearity manifests in global climate models, which robustly produce a global-mean longwave clear-sky (LWCS) feedback of 1.9 W/m2/K, consistent with idealized single-column models (Koll & Cronin, 2018, https//:doi.org/10.1073/pnas.1809868115). However, there is considerable spatial variability in the LWCS feedback, including negative values over tropical oceans (known as the “super-greenhouse effect”) which are compensated for by larger values in the subtropics/extratropics. Therefore, it is unclear how the idealized single-column results are relevant for the global-mean LWCS feedback in comprehensive climate models. Here we show with a simple analytical theory and model output that the compensation of this spatial variability to produce a robust global-mean feedback can be explained by two facts: (1) When conditioned upon free-tropospheric column relative humidity (RH), the LWCS feedback is independent of RH, and (2) the global histogram of free-tropospheric column RH is largely invariant under warming.
KW - Atmospheric radiative transfer
KW - Climate feedback
KW - Climate sensitivity
KW - Greenhouse effect
KW - Relative humidity
KW - Water vapor feedback
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UR - http://www.scopus.com/inward/citedby.url?scp=85090898561&partnerID=8YFLogxK
U2 - 10.1029/2020GL089235
DO - 10.1029/2020GL089235
M3 - Article
AN - SCOPUS:85090898561
SN - 0094-8276
VL - 47
JO - Geophysical Research Letters
JF - Geophysical Research Letters
IS - 17
M1 - e2020GL089235
ER -